Blood Journal
Leading the way in experimental and clinical research in hematology

JAM-A protects from thrombosis by suppressing integrin αIIbβ3-dependent outside-in signaling in platelets

  1. Meghna U. Naik1,
  2. Timothy J. Stalker2,
  3. Lawrence F. Brass2, and
  4. Ulhas P. Naik1,3
  1. 1Department of Biological Sciences, University of Delaware, Newark, DE;
  2. 2Department of Medicine, University of Pennsylvania, Philadelphia, PA; and
  3. 3Delaware Biotechnology Institute, University of Delaware, Newark, DE


Mounting evidence suggests that agonist-initiated signaling in platelets is closely regulated to avoid excessive responses to injury. A variety of physiologic agonists induce a cascade of signaling events termed as inside-out signaling that culminate in exposure of high-affinity binding sites on integrin αIIbβ3. Once platelet activation has occurred, integrin αIIbβ3 stabilizes thrombus formation by providing agonist-independent “outside-in” signals mediated in part by contractile signaling. Junctional adhesion molecule A (JAM-A), a member of the cortical thymocyte marker of the Xenopus (CTX) family, was initially identified as a receptor for a platelet stimulatory mAb. Here we show that JAM-A in resting platelets functions as an endogenous inhibitor of platelet function. Genetic ablation of Jam-A in mice enhances thrombotic function of platelets in vivo. The absence of Jam-A results in increase in platelet aggregation ex vivo. This gain of function is not because of enhanced inside-out signaling because granular secretion, Thromboxane A2 (TxA2) generation, as well as fibrinogen receptor activation, are normal in the absence of Jam-A. Interestingly, integrin outside-in signaling such as platelet spreading and clot retraction is augmented in Jam-A–deficient platelets. We conclude that JAM-A normally limits platelet accumulation by inhibiting integrin outside-in signaling thus preventing premature platelet activation.

  • Submitted December 8, 2011.
  • Accepted January 13, 2012.
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